The present invention relates to a structure having an LED package fixed to a heat releasing casing and a light fixture provided with the structure.
Conventionally, a lighting structure includes a metal fitted member fitted to a constructed object, a light control body that controls light emitted from an LED package, a cover body having a base substrate sandwiched between the metal fitted member and the light control body, and a light fixture that incorporates the lighting structure.
One example of a conventional lighting structure is disclosed in Japanese Patent Application No. JPA 2005-71711, in which the structure and the light fixture provided with the structure can release heat from the LED package and can position the base substrate in a predetermined position.
However, as shown in FIG. 13, similar to the structure and the light fixture described in JPA 2005-71711 described above, a structure 150 formed by mounting an LED package 151 on a base material 152 of resin or metal through soldering and fitting them onto a casing 153 is suggested.
Moreover, as shown in FIG. 14, a structure 160 formed by mounting an LED package 163 on a base material 161 on which an LED chip 162 is mounted and fitting them to a casing 165 with, for example, a heat conducting sheet 164 or an adhesive agent is suggested.
However, such conventional structures 150 and 160 have a common problem. In the case where the casings 153 and 165 are formed of metal such as aluminum for the purpose of improving heat release performance, and the base materials 152 and 161 are formed of resin such as glass epoxy, the base materials 152 and 161 have poor heat conductivity and heat is not efficiently transferred to the casings 153 and 165. This increases the temperatures of the LED packages 151 and 163, which results in deterioration in light emission efficiency of the LED packages 151 and 163.
To solve such a conventional problem, application of a base material of metal using a material such as copper or aluminum improves heat release performance of the LED package but deteriorates the voltage resistance because the thickness of the insulation layer of the base material is small.
In such a case, a heat conducting sheet with a high voltage resistance is fitted to a rear surface of the base material. However, this heat conducting sheet is soft itself and thus flexure occurs between a screw-fixed portion and a screw-non-fixed portion, thereby causing deformation of the base material, which raises a long-term reliability problem. In addition, heat conductivity of the heat conducting sheet with high voltage resistance is not high, thus impeding heat conduction in some cases.
For the LED package, low consumed power does not cause a serious problem but as a result of automatic fixation of the LED package with an increase in consumed power, following heat generation of the LED package, extension of the metal material itself occurs due to thermal expansion. A small gap is created between the metal material and a hard material having both thermal conductance and electric insulation properties which impedes heat release due to the thermal insulating effect of air.
Further, even when the extension due to the thermal expansion is minimized following the automatic firm fixation, the small gap is created by, for example, the slight deformation of the metal base material, which impedes the heat release.
A possible solution to such a problem is using a plastic fluid or an adhesive agent having addition of particles with high thermal conductivity in a manner such as to fill the small gap. However, the excess plastic fluid or adhesive agent protrudes from the margins of the LED package, which therefore requires an additional material removal process, resulting in an increase in labor costs.
In addition, the conventional structures 150 and 160 require a large-scale facility such as a special reflow device for soldering to the base materials 152 and 161. Therefore, the conventional structures 150 and 160 have cost disadvantages.
Further, the conventional structures 150 and 160 may experience temperatures' of approximately 260° C. in reflow. Therefore, the conventional lighting structures 150 and 160 may experience quality deterioration as a result of degradation of an initial optical beam of the LED packages 151 and 163 due to heat deterioration of the members forming the LED packages 151 and 163.